Oxidized coenzyme Q10, which is a benzoquinone derivative widely distributed in the living world, is also called vitamin Q due to its function like a vitamin, and is a component that rejuvenates the body as a nutrient source that brings weak cell activity to a healthy state. On the other hand, reduced coenzyme Q10 is a two-electron reduction form of oxidized coenzyme Q10, and oxidized coenzyme Q10 is an orange crystal, whereas reduced coenzyme Q10 is a white crystal. Reduced coenzyme Q10 and oxidized coenzyme Q10 are localized in mitochondria, lysosome, golgi apparatus, microsome, peroxisome, cellular membrane and the like, and are indispensable substances for the maintenance of biological functions, which are known to be involved in the activation of ATP production, antioxidant action in the body and stabilization of membrane as a constituent component of the electron transport system.
As a production method of reduced coenzyme Q10, it is known to be obtained, for example, by a method comprising producing coenzyme Q10 by a conventionally known method such as synthesis, fermentation, extraction from a naturally occurring substance and the like, and concentrating a reduced coenzyme Q10 fraction in an eluate from chromatography and the like (patent reference 1: JP-A-H10-109933). The patent reference 1 describes that, in this case, oxidized coenzyme Q10 contained in the above-mentioned reduced coenzyme Q10 may be reduced with a reducing agent such as sodium borohydride, sodium hydrosulfite (sodium dithionite) and the like, and concentrated by chromatography, and that the reduced coenzyme Q10 can also be obtained by a method comprising reacting existing highly pure coenzyme Q10 with the above-mentioned reducing agent.
In addition, a method of reducing oxidized coenzyme Q10 to reduced coenzyme Q10 by using ascorbic acid or its analogue(s) is also known (non-patent document 1: J. Am. Chem. Soc., 1990, 116, 9440-9447). In this document, a reduction reaction of oxidized coenzyme Q10 is performed in a mixed solvent of ethanol/water in the presence of sodium hydroxide.
On the other hand, the present inventors have also filed some patent applications relating to reduction reaction of oxidized coenzyme Q10 by using ascorbic acid or its analogue(s) as reducing agent (e.g., patent documents 2-4: WO03/006408, WO03/006409, WO03/032967). These patent documents describe that oxidized coenzyme Q10 can be reduced by using ascorbic acids or its analogue(s), a water-soluble organic solvent or water can be used as solvents, and a basic substance and bisulfite are added as reaction promoters.
However, oxidized coenzyme Q10, which is the starting material of these reduction reactions, and reduced coenzyme Q10, which is the resultant product, do not dissolve in water. Therefore, when water is used during reduction reaction, 2-phase reactions are generally employed requiring a large amount of water, which is not entirely advantageous from the aspects of volume efficiency and the like. As mentioned above, addition of a reaction promoter such as a basic substance, bisulfite and the like is generally proposed to shorten the reaction time of reduction reactions by using ascorbic acids or its analogue(s). When such a reaction promoter is used, incorporation of a separate step of removing the above-mentioned reaction promoter before obtaining reduced coenzyme Q10 also needs to be considered.    patent document 1: JP-A-10-109933    patent document 2: WO03/006408    patent document 3: WO03/006409    patent document 4: WO03/032967    non-patent document 1: J. Am. Chem. Soc., 1990, 116, 9440-9447